Study On Medium Chain Fatty Acids Production From Food Waste Anaerobic Fermentation

With the sustained and rapid development of China's economy,people's living standards are increasing,and the output of kitchen waste is also increasing year by year.If you do not properly dispose of kitchen waste,it will seriously harm the environment and human health.As an important intermediate product of anaerobic digestion reaction,short-chain fatty acid and lactic acid are both energy materials and industrial raw materials,and have high practical value.The anaerobic fermentation of kitchen waste as a substrate produces short-chain fatty acids and lactic acid,which can realize the recycling of kitchen waste and avoid environmental pollution.However,the composition of the fermentation broth is complicated,and the solubility of the short-chain fatty acid and lactic acid is high,so that the purification cost thereof is greatly increased.Medium-chain fatty acids have higher energy density and lower solubility than short-chain fatty acids,and are widely used in industrial applications.The microorganism can use ethanol,lactic acid or the like as an electron donor to cause chain growth of the short-chain fatty acid to form a medium-chain fatty acid.Therefore,the use of anaerobic fermentation of kitchen waste to produce short-chain fatty acids and lactic acid,and then upgrade the short-chain fatty acids in the fermentation broth to medium-chain fatty acids,to achieve the anaerobic fermentation of food waste in the production of medium-chain fatty acids has a high practical significance.The kitchen garbage has high carbohydrate content,and it can be used as a substrate for anaerobic fermentation.The C/N ratio may be high,and the microbial species in the kitchen waste may be less.Therefore,the residual activated sludge and the kitchen waste are co-fermented.Production of short-chain fatty acids,lactic acid.As one of the fermentation products,lactic acid can be used as an electron donor for chain-growth reaction,and its oxidation products,acetic acid,propionic acid,etc.,can serve as electron acceptors for chain-growth reactions.Therefore,when the short-chain fatty acid and lactic acid are co-fermented by using kitchen waste and residual activated sludge,the maximum lactic acid yield is obtained as an indicator and the reaction conditions are optimized.The results showed that the anaerobic fermentation was carried out with the kitchen waste as the sole substrate.The concentration of the kitchen waste had little effect on the reaction.At 20g/L,30g/L and 40g/L,the lactic acid production rate and yield were close to each other;It can increase the rate of lactic acid production,but has little effect on the yield.At high temperatures,lactic acid production is about half that of medium temperature conditions.When the activated sludge and the kitchen waste were co-fermented to produce lactic acid,the rate of lactic acid production increased rapidly,and when the kitchen waste accounted for 85% of the total solid content,the lactic acid production rate and yield were the highest.The higher the pH value,the faster the rate of lactic acid production.Compared with the kitchen substrate as the sole substrate,the lactic acid production rate is different under different pH conditions,but has little effect on the lactic acid yield.The maximum lactic acid yield was obtained at 55 ° C and pH 7,and it was considered that the high temperature promoted the hydrolysis of the substrate more than the inhibition of the microbial activity.When the medium-chain fatty acid is produced by the lactic acid-rich fermentation broth,the reaction substrate is a lactic acid fermentation liquid,and the domesticated activated sludge is inoculated.First,investigate whether the fermentation broth can produce medium-chain fatty acids without adding other drugs,and investigate the effect of lactic acid concentration on the production of chain acid.The results showed that the fermentation reaction was the only substrate,and the chain growth reaction could occur.The product was butyric acid and valeric acid.With the increase of substrate concentration,the formation rate and maximum concentration of butyric acid and valeric acid increased,but no hexanoic acid was formed.Chain fatty acids.Then,the effect of the external electron acceptor acetic acid on the fatty acids in the system was investigated.The results showed that the addition of a certain proportion of acetic acid could increase the rate and concentration of butyric acid and valeric acid,and the ratio of lactic acid to acetic acid was 4/1.A small amount of hexanoic acid was formed at 3/1.Finally,the effects of combined electron donor lactic acid and ethanol on the production of medium chain fatty acids were investigated.The results showed that with the addition of ethanol to form a combined electron donor,the product began to produce heptanoic acid,and the concentration of hexanoic acid also increased significantly,indicating co-fermentation.It promotes the concentration of the product and the production of fatty acids with longer carbon chains.